The present invention relates to a driving tool for turning a screwthreaded member, particularly a hand tool, of the type comprising a head having at least two contact surfaces for driving the screwthreaded member by at least partial complementarity of form, and driving means for turning the head. The head behaves overall as a single piece when turning a screwthreaded member. The head includes a connecting region between the contact surfaces and the parts that transmit, to the contact surfaces, a turning force applied to the driving means. The connecting region is situated between the force transmitting parts and the contact surfaces.
The present invention applies, for example, to flat open-ended wrenches.
The head of such a wrench has two rigid open jaws, each of which has a contact surface for a screwthreaded member such as a nut. The two contact surfaces are opposite each other.
When a wrench of this kind is used to transmit a turning force to a nut, the jaws deform in such a way that the contact surfaces move apart. The nut therefore turns relative to the jaws. This modifies the pressure points between the nut and the jaws such that the force vectors (which are theoretically parallel) corresponding to the turning force move toward each other. This means that, for a given turning force, the magnitude of the corresponding forces increases. This increase leads in turn to an increase in the bending of the jaws. The phenomenon is self-amplifying and, above a certain value, there is total rotation of the nut in the jaws, often with destruction of the latter. The nut can then be said to have become in effect a cam, causing the wrench to burst.
The phenomenon therefore limits the turning forces that can be transmitted by any such flat open-ended wrench. This phenomenon is present in a general way in tools in which, unlike vices, for example, the clamping force of the contact surfaces is not independent of the turning force.
It is an object of the present invention to solve this problem by providing a tool of the aforementioned type capable for example of exerting increased turning forces on a screwthreaded member.
To this end, the subject of the present invention is a tool of the aforementioned type, characterized in that the head is designed so that the action of the driving means on the force transmitting parts tends to deform the geometry of the head such that the contact surfaces move toward each other when a driving force for turning a screwthreaded member is applied through the driving means.
In various particular embodiments, the tool can include one or more of the following characteristics, taken in isolation or in any of the technically possible combinations:
the head is designed so that the action of the driving means tends to deform the head elastically,
the driving means for turning the head comprise an actuating member for actuating the head,
the actuating member of the head is able to move relative to the latter in order to tend to move the contact surfaces toward each other, by lever action or by cam action on the force transmitting parts, when a driving force is applied to the actuating member to turn a screwthreaded member,
the head has a generally H configuration and comprises two arms connected by a central web, a distal region of each arm having one of the contact surfaces and the proximal regions of the arms forming said force transmitting parts, the two arms are able to move with respect to each other by deformation of the central web in order to move the contact surfaces toward each other by separation of proximal regions of the arms, and a distal region of the actuating member is positioned between the proximal regions of the arms in order to push them apart, by lever action or by cam action, when a driving force is applied to the actuating member to turn a screwthreaded member,
the actuating member is connected to the head by a flexible connection,
the flexible connection comprises a deformable part formed integrally with the head and the actuating member,
the actuating member and the head are separated or separable,
the tool comprises removable means connecting the head to the actuating member,
the actuating member can pivot with respect to the head,
the actuating member is part of a torque-measuring tool,
the tool comprises means for adjusting the tendency of the head to deform under the action of the driving means,
the head comprises two open jaws, each of which has at least one of the contact surfaces, and
the flexible connection is made of elastomer.
Here, the expression xe2x80x9chead having at least two contact surfaces for turning a screwthreaded member by at least partial complementarity of formxe2x80x9d denotes a head capable of driving such a member due to the fact that their respective shapes, which may be for example polygonal shapes, do not allow relative rotation.
In the present invention, the head also behaves functionally overall as a single piece of sufficient stiffness that, when in use, the functional geometry of the head remains essentially unchanged, except under the effect of deformation under load and the compensation of the latter according to the invention as will be described below.